REACTIONS OF FISHES TO SALTS 249 



c. Sodium chloride. This was the first salt to be experimented 

 with at the University of lUinois and a large number of experi- 

 ments (46 in all) was performed with it, as the reactions of the 

 fishes were not what was at first expected. Experiments were 

 run in aerated (neutral) water, in moderately, acid water (8-10 

 cc. per liter) and in strongly acid water (18 cc. CO2 per liter). 



It had been noted that the f shes became sluggish when kept 

 in the aerated water, and because they reacted positively to the 

 NaCl in the gradients in this neutral water, the experiments 

 were repeated in acid water to make the results certain. The 

 fishes were positive to the NaCl half of the tank in all three kinds 

 of water, but were markedly most positive in the most acid water. 

 They are negative to this water alone, because of its marked 

 acidity. The increase in positiveness to the NaCl in the acid 

 water must be due to the fact that the salt antagonizes the 

 stimulating action of the acid and thus the fishes selected the 

 portion of the tank where they were the least stimulated, as they 

 did in the case of the KCl gradient in acid water. 



In an attempt to drive the fishes out of the salt end, the NaCI 

 concentration was increased to 0.02N but without diminishing 

 the positive reaction. In the strongly acid water the fishes were 

 found to give a positive reaction to as small a concentration of 

 NaCl as O.OOIN though the reaction to this low concentration 

 was not so definite as with the higher concentrations. The reac- 

 tion to NaCl varied somewhat with the species; the crappies 

 and bull-heads were positive . in all three kinds of water while 

 the blue-gills were positive in the neutral and strongly acid water 

 but were indifferent to negative, in the moderately acid water. 



Ten experiments with O.OIN NaCl, in distilled water, were 

 run to check those with the tap water. The results show the 

 fishes to be markedly positive to the NaCl in distilled water gra- 

 dients; this positiveness is not as great as in the acid water, but 

 is great enough to show conclusively that the fishes used are 

 positive to NaCl in concentrations very little lower than O.OIN. 



d. Calcium chloride. Calcium chloride was the first salt used 

 at Chicago in the gradient experiments. It was found that 

 normal fishes (large rock bass are exceptions) are negative to 



